This invention relates to the discovery that Epstein Barr virus may be found in the cell free fluid of a patient""s blood and when such virus is found and the patient suffers from gastritis, that patient has a predisposition to progress from gastritis to gastric cancer.
It is known that tumour-derived DNA can be released by cancer cells of a variety of tumours (Anker et al., Cancer Metastasis Rev. 18: 65-73 (1999)). Examples include oncogene mutations from pancreatic carcinoma (Anker et al., Gastroenterology. 112: 4-1120 (1997)), microsatellite alterations in lung cancer (Chen et al., Nature Medicine. 2: 3-1035 (1996)) and epigenetic changes from liver cancer (Wong et al., Cancer Res. 59: 3 (1999)). In addition, virus DNA has been found in the circulation of a number of cancers known to be associated with virus infection. Examples include Epstein-Barr virus (EBV) DNA from nasopharyngeal cancer (Mutirangura et al., Clin Cancer Res. 4: 665-9 (1998); Lo et al., Cancer Res. 59: 1188-91 (1999)) and certain lymphomas (Lei et al., Br J Haematol. 111: 239-46 (2000); Gallagher et al., Int J Cancer. 84: 442-8 (1999); Drouet et al., J Med Virol. 57: 383-9 (1999)), and human papillomavirus DNA from head and neck cancer (Capone et al., Clin Cancer Res. 6: 4171-5 (2000)).
Recently, much interest has been focused on the presence of tumor-derived DNA in the plasma and serum of cancer patients (Chen, X. Q. et al., Nat. Med., 2: 1033-1035 (1996); Nawroz, H. et al., Nat. Med., 2: 1035-1037 (1996)). For virally-associated cancers, cell-free tumor-associated viral DNA has been detected in the plasma and serum of patients (Mutirangura, A. et al., Cancer Res., 4: 665-669 (1998); Lo, Y. M. D. et al., Clin. Cancer Res., 59: 1188-1191 (1999); Capone, R. B. Clin. Cancer Res., 6: 4171-4175 (2000)). One important virus which has been associated with many types of malignancy is the Epstein-Barr virus (EBV) (Cohen, J. I. N. Engl. J Med., 343: 481-492 (2000)). Epstein-Barr virus (EBV) is a human herpesvirus that infects the majority of the human population. EBV is commonly transmitted by saliva and established latent infection in B lymphocytes where it persists for the lifetime of the host. In this regard, circulating EBV DNA has been detected in the plasma and serum of patients with nasopharyngeal carcinoma (NPC) (Mutirangura, A. et al., Cancer Res., 4: 665-669 (1998); Lo, Y. M. D. et al., Clin. Cancer Res., 59: 1188-1191 (1999)) and certain lymphoid malignancies (Lei, K. I. et al., Br. J Haematol., 111: 239-246 (2000); Drouet, E. et al., J. Med. Virol., 57:383-389 (1999); Gallagher, A. et al., Int. J. Cancer, 84:442-448 (1999)).
EBV infection has also been reported to be associated with a proportion of gastric carcinomas (Shibata, D. et al., Am. J. Pathol., 140:769-774 (1992)). In Hong Kong, approximately 10% of gastric carcinoma cases have been found to be associated with EBV infection (Yuen, S. T. et al., Am. J. Surg. Pathol., 18:1158-1163 (1994)).
The present invention provides methods for detecting EBV DNA in the sera of patients with gastric carcinoma and correlating the amount of EBV DNA so detected into clinical diagnosis or prognosis.
In a first aspect, the present invention features methods for diagnosing, detecting, monitoring and determining the prognosis of gastric cancer in a patient. The methods feature detecting or determining the amount of Epstein Barr Virus DNA (EBV DNA) present in the serum or plasma of gastric cancer patients. Accordingly, the present invention have broad applicability in clinical medicine.
The methods according to the present invention are also applicable for diagnosing, detecting, monitoring and determining the prognosis of non-head and neck and lymphoid malignancies, such as breast cancer. These neoplasms have been associated with EBV infection as has gastric cancer.
The methods according to the present invention are also applicable for diagnosing, detecting, monitoring and determining the prognosis of gastritis. EBV DNA can be detected in the plasma and serum of patients having non-neoplastic gastric diseases, such as gastritis. In turn, gastritis has been linked to gastric cancer. The invention further comprises patients that can be or have been diagnosed with gastric cancer and the cancer cells are free of EBV nucleic acid or contain EBV.
The methods according to the present invention generally comprise the steps of (1) obtaining a blood sample from a patient, (2) extracting DNA from the blood sample, (3) measuring the amount of circulating EBV DNA present in the blood sample, and (4) comparing the amount of circulating EBV DNA present in the blood sample to a control.
Preferably, the blood sample is a non-cellular fluid sample. By non-cellular we mean that the sample is either blood sera where the cells are extracted by clotting and separation of the cells from the remaining fluid or by inhibiting clotting and centrifuging the fluid fraction (plasma). The EBV DNA is measured from the fluid fraction. When EBV is found in the fluid of a non-cellular sample, it is understood that the infection is active and infected cells releasing EBV.
In a second aspect, the present invention features diagnostic kits comprising suitable reagents for detecting EBV DNA in the serum or plasma of patients. The kits according to the present invention may further comprise one or more of a device for obtaining a blood sample from a patient, a means to separate the EBV DNA from the blood sample and a means to quantify the amount of EBV DNA present in the blood sample. Such kits are useful for diagnosing, detecting, monitoring and determining the prognosis for gastric cancers and gastritis